The present invention relates to a method for processing sensor data for a driver assistance system and to a sensor apparatus.
There are different driver assistance systems which assist the driver of a motor vehicle with partially automated or fully automated control of the motor vehicle. Such driver assistance systems are lane change assistants, braking assistants, emergency steer assistants or driver assistance systems for automated driving of a motor vehicle.
So that driver assistance systems can be used to control a vehicle and, in particular, can control the vehicle, automatic methods have been developed and can be used to detect objects and to enter them in an occupancy grid. The individual objects are often detected using different sensors, for example a radar, a lidar, a camera or an infrared sensor.
The data from the different sensors are combined to form the occupancy grid in a central control device.
The occupancy grid must be created in real time so that the driver assistance system can create collision-free trajectories.
Since a plurality of objects are respectively detected by the different sensor apparatuses at the same time, large volumes of data arise and must be transmitted from the sensor apparatuses to the central control device. A significant portion of the computing power of the central control device is used to communicate with the individual sensor apparatuses.
The driver assistance systems for motor vehicles can be subdivided into two groups: the safety driver assistance systems and the comfort driver assistance systems.
The safety driver assistance systems assist the driver in a hazardous situation. Such safety driver assistance systems are, for example, the anti-lock braking system (ABS) and automatic driving stability systems. There are also safety driver assistance systems which take into account data relating to automatically detected objects, for example emergency braking assistants which detect objects by means of a radar and trigger emergency braking in a hazardous situation. The advantage of such safety driver assistance systems is that they can react considerably more quickly than a person and can also detect the driving situation without interruption. Persons can sometimes be distracted, which is often the trigger for hazardous situations. The aim of safety driver assistance systems is to prevent an accident or at least to minimize the consequences of an accident.
In contrast, comfort driver assistance systems are intended to assist the driver when driving and to simplify the driving of a vehicle. A typical example of a comfort driver assistance system is an automatic adaptive cruise control system. In a similar manner to that in the case of the emergency braking assistant, an object in front of the respective vehicle is detected using a radar and the distance to this object is determined. Depending on the detected distance and the current driving speed, the brakes and the drive are controlled in such a manner that a predetermined distance is complied with. This system can be used to follow another vehicle without having to accelerate or brake. The driving of a vehicle is therefore simplified.
The invention is based on the object of providing a method for processing sensor data for a driver assistance system for a motor vehicle and of providing a sensor apparatus, with which method and sensor apparatus the sensor data are efficiently transmitted between sensor apparatuses and a central control device and little computing power is used in the central control unit.
In a method according to the invention for processing sensor data for a comfort driver assistance system for a motor vehicle, sensor data describing the respective location of objects are acquired. The coordinates of the objects are extracted from the sensor data, an inner side of the object, on which the motor vehicle is intended to drive past the object, being defined. The current speed of the motor vehicle is recorded. A region which can be traveled on and is in front of and/or behind each of the objects in the direction of travel of the motor vehicle is distinguished from a region which cannot be traveled on. The region which can be traveled on is referred to as the object travel region below. The boundary between the object travel region and the region which cannot be traveled on is a boundary line which extends beyond the object to the front and/or to the rear along the inner side of the object in the direction of travel. Data relating to this boundary line are forwarded from a sensor device to a control device of the comfort driver assistance system instead of the sensor data describing the object.
The object travel region is therefore defined by the boundary line. The volume of data to be transmitted between the sensor device and the control device can be considerably reduced by transmitting a boundary line for the object travel region instead of an exact description of the detected objects.
In a comfort driver assistance system which processes information relating to automatically detected objects, the detection and processing must be carried out in real time and secure transmission of all necessary data from the sensor devices to the control device must be ensured. The object travel region excludes the region which cannot be traveled on, with the result that objects which are in this region which cannot be traveled on any longer appear and do not produce any further data. The description of the object travel region by means of the boundary line gives rise to considerably fewer data items than the description of individual objects by means of coordinates, which is why the data relating to the boundary lines can be transmitted between the sensor apparatus and a central control device more efficiently and with less computational effort.
The invention is based on the knowledge that comfort driver assistance systems which process information relating to automatically detected objects in the environment of the vehicle in order to automatically control the vehicle, in particular in order to automatically steer the vehicle, do not require an exact description of the detected objects, but only a reliable description of the region which can be traveled on. For example, it is not necessary to individually describe individual roadside posts, but rather it suffices to determine a boundary line, which extends along the inner side of a plurality of roadside posts, instead of the individual geometric description of the roadside posts. In principle, it is possible to leave a road between two roadside posts, which can also make sense in an emergency in order to swerve into a meadow adjacent to the road in a hazardous situation, for example. However, this is not useful for comfort-oriented control since normally there is no desire to leave the road with a vehicle in the normal driving mode. In other words, this means that a comfort driver assistance system does not require an exact description of the entire region which can be theoretically traveled on, but rather only a reliable description of the region which can be usefully traveled on. This region which can be traveled on may be smaller than the entire region which can be theoretically traveled on. It goes without saying that it must not contain any obstacles. A comfort driver assistance system differs in this respect from a safety driver assistance system which requires information relating to the entire region which can be theoretically traveled on. If a safety driver assistance system detects an obstacle on the regular road, it also requires information regarding whether it is possible to swerve onto a meadow adjoining the road in order to be able to initiate a swerving operation.
The boundary line can therefore be determined in different ways as long as it is ensured that the object travel region comprises a large part of the region which can be traveled on during normal operation.
The boundary line can be determined, for example, by connecting the inner sides of adjacent objects. In this case, the boundary line may connect the objects in a straight line. The boundary line may also be curved. It may be represented by a spline function in the regions between the objects, for example, which spline function connects those edges of the adjacent objects which are on the inner sides to one another. The connection of the inner sides of a plurality of objects to form a boundary line is preferably carried out in the sensor apparatus.
The boundary line may also be a trajectory which describes a path of the motor vehicle which, coming from the outside in front of the object in the direction of travel, leads past the inside of the object at a minimum distance with a maximum steering angle, and/or describes a path which leads outward from the object with a maximum steering angle for the current driving speed after the object, the maximum steering angle being determined on the basis of the speed of the motor vehicle.
The boundary line is preferably determined only if the vehicle is moving at a predetermined minimum speed. This minimum speed is, for example, 10 km/h and is, in particular, 30 km/h. At high speeds, new objects are detected at short intervals of time since the motor vehicle is moving, with the result that the volume of data describing the detected objects is greater at high speeds than at low speeds. If trajectories are intended to be automatically calculated in order to autonomously steer the motor vehicle, they are usually calculated in sections for a particular section in front of the motor vehicle. They must be recalculated at shorter intervals at a high speed since they are covered more quickly. This means that, the higher the speed, the more difficult it is to detect the objects in real time and to transmit the corresponding data to the central control device and to process said data there.
The inner side of the objects is preferably determined as that side of the objects on which a trajectory which describes the movement of the motor vehicle in the direction of travel passes along. For this purpose, the trajectory is stipulated in the direction of travel of the motor vehicle starting from the current location of the motor vehicle. The trajectory may be rectilinear or may be formed according to the course of a route defined by means of a navigation system.
Automatic object recognition is preferably carried out, each of the detected objects respectively being at least assigned to a class of a predetermined set of classes of objects, for example road boundary posts, a road sign and another vehicle. In Germany, the road boundary posts usually have a white reflector and have an orange reflector at intersections. There is preferably a class for boundary posts which are not arranged at intersections (white reflectors) and boundary posts which are arranged at intersections (orange reflectors). If the boundary line is determined by connecting adjacent objects, a boundary post for an intersection represents an end region of such a boundary line since a further road joins between two boundary posts for an intersection, onto which road it is possible to turn off.
The object recognition is preferably carried out by means of an image analysis.
Moving objects can be detected by means of a speed measurement for measuring the relative speed between the motor vehicle and the object.
It is also possible to distinguish between moving and non-moving objects by means of such a speed measurement.
Moving objects, for example other motor vehicles and cyclists and pedestrians, are preferably not taken into account as obstacles which restrict the region which can be traveled on when determining the region which can be traveled on. In particular, other motor vehicles generally travel on a region which can be traveled on, with the result that they indicate to the system where the region which can be traveled on is situated. Therefore, it may also be expedient to take into account moving objects when determining the inner side of static objects.
A vehicle travel region can be determined, the boundaries of which are defined by two trajectories each describing a theoretical path of the motor vehicle running to the right or left in the direction of travel from the current location of the motor vehicle with a maximum steering angle. The vehicle travel region is between these two trajectories, in which case objects and an object travel region outside this vehicle travel region can be ignored.
The vehicle travel region is preferably calculated in the central control device and is combined with the object travel regions to form a movement region.
The calculated vehicle travel region can also be transmitted from the central control device to the sensor apparatus or can be calculated in the sensor apparatus itself. The sensor apparatus can then determine, with the aid of the determined vehicle travel region, whether particular objects are outside the vehicle travel region. These objects can then be ignored during further processing and only the descriptions of the objects inside the vehicle travel region are transmitted to the central control device.
The currently measured driving speed can be used as the speed of the motor vehicle for determining the maximum steering angle. Alternatively, it is possible to use the currently measured driving speed minus a maximum deceleration.
The width of the motor vehicle is preferably taken into account when determining the trajectories. This can be effected, on the one hand, by virtue of the fact that the trajectories for the vehicle travel region begin on the lateral edge of the motor vehicle and the trajectories of the object travel region describe the movement of the corresponding lateral edge region of the motor vehicle. On the other hand, the trajectories may describe the movement of a center point of a motor vehicle. A center point is, for example, the center of gravity of the motor vehicle or the center of a base of the motor vehicle. The trajectories which describe the object travel regions should then be accordingly offset by half a width from the edge of the corresponding objects in the direction of the vehicle.
A sensor apparatus according to the invention comprises a sensor element and a processor controller for processing sensor data for a comfort driver assistance system for a motor vehicle. The sensor element is designed to acquire sensor data describing a respective location of objects. The processor controller is designed to extract coordinates of the objects from the sensor data, an inner side of the object, on which the motor vehicle is intended to drive past the object, being determined. The processor controller is designed in such a manner that a region which can be traveled on and is in front of and/or behind each of objects in the direction of travel of the motor vehicle is distinguished from a region which cannot be traveled on. The region which can be traveled on is referred to as the object travel region below. The boundary between the object travel region and the region which cannot be traveled on is defined by a boundary line which extends beyond the object to the front and/or to the rear along the inner side of the object in the direction of travel. Data relating to this boundary line are provided, instead of the sensor data describing the object, for forwarding to the comfort driver assistance system.
Such a sensor apparatus is already used to process the sensor data acquired by the sensor elements to such an extent that their volume of data is considerably reduced in comparison with a conventional description of objects, with the result that fast and simple transmission to a central control device of the comfort driver assistance system as possible.
The sensor elements may be in the form of a radar, a lidar, a camera, and/or an ultrasonic sensor, for example.
A radar has a wide range and, in addition to location information, also provides speed information relating to the individual objects. However, the angular resolution of a radar is rather low. A lidar, which is also referred to as a laser scanner, has a very high resolution. However, the sensor signals are impaired in the case of poor visibility caused by fog or spray on the road. A camera has a high angular resolution, but the exact distance can be estimated only with a considerable amount of computational effort. The method of operation of a camera is considerably impaired in the case of backlighting. An ultrasonic sensor is used for the near field detection of objects. The individual sensor types each have strengths and weaknesses, with the result that the objects in the environment of the motor vehicle are preferably detected using different sensor types.
The term “sensor element” may also comprise any data source which provides data for describing objects. Such a data source may also be a digital map in which the objects are entered.
The sensor data from the sensor apparatus are intended to be acquired and forwarded as precisely as possible. When processing the sensor data in the sensor apparatus, there is therefore no intention to add a safety range or safety tolerance. This can then be carried out in the driver assistance system.
A system according to the invention for processing sensor data for a driver assistance system for a motor vehicle comprises at least one sensor apparatus according to the invention and a central control device which is connected to the sensor apparatus.
The central control device may be designed to create an occupancy grid. The occupancy grid can be used to automatically determine a trajectory for autonomously steering the motor vehicle.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.